U.S. patent number 7,723,223 [Application Number 12/232,958] was granted by the patent office on 2010-05-25 for method of doping transistor comprising carbon nanotube, method of controlling position of doping ion, and transistors using the same.
This patent grant is currently assigned to Samsung Electronics Co., Ltd.. Invention is credited to Jae-young Choi, Un-jeong Kim, Young-hee Lee, Woo-jong Yu.
United States Patent |
7,723,223 |
Kim , et al. |
May 25, 2010 |
Method of doping transistor comprising carbon nanotube, method of
controlling position of doping ion, and transistors using the
same
Abstract
Provided are a method of doping a carbon nanotube (CNT) of a
field effect transistor and a method of controlling the position of
doping ions. The method may include providing a source, a drain,
the CNT as a channel between the source and the drain, and a gate,
applying a first voltage to the gate, and adsorbing ions on a
surface of the CNT.
Inventors: |
Kim; Un-jeong (Busan,
KR), Lee; Young-hee (Suwon-si, KR), Choi;
Jae-young (Suwon-si, KR), Yu; Woo-jong (Gwangju,
KR) |
Assignee: |
Samsung Electronics Co., Ltd.
(Gyeonggi-do, KR)
|
Family
ID: |
41163246 |
Appl.
No.: |
12/232,958 |
Filed: |
September 26, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090256175 A1 |
Oct 15, 2009 |
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Foreign Application Priority Data
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Apr 11, 2008 [KR] |
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10-2008-0033882 |
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Current U.S.
Class: |
438/585;
438/197 |
Current CPC
Class: |
B82Y
30/00 (20130101); B82Y 40/00 (20130101); C01B
32/168 (20170801); B82Y 10/00 (20130101); H01L
51/002 (20130101); H01L 51/0008 (20130101); H01L
51/0048 (20130101); H01L 51/0545 (20130101) |
Current International
Class: |
H01L
21/336 (20060101) |
Field of
Search: |
;257/44,E29.07,E21.409,46,104 ;427/561 ;423/593.1
;438/99,105,197,300,585 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Potter; Roy K
Attorney, Agent or Firm: Harness, Dickey & Pierce,
P.L.C.
Claims
What is claimed is:
1. A method of doping a carbon nanotube (CNT) of a field effect
transistor comprising: providing a source, a drain, the CNT as a
channel between the source and the drain, and a gate on a
substrate; applying a first voltage to the gate; and adsorbing ions
on a surface of the CNT.
2. The method of claim 1, wherein adsorbing the ions includes
dropping a nitronium hexafluoroantimonate (NHFA) solution onto a
surface of the CNT.
3. The method of claim 2, wherein the first voltage is a positive
voltage, the ions are nitronium ions, and the CNT is p-doped.
4. The method of claim 2, wherein the first voltage is a negative
voltage, the ions are hexafloroantimonate ions, and the CNT is
n-doped.
5. The method of claim 2, wherein a solvent of the NHFA solution is
methanol.
6. The method of claim 2, further comprising: removing the surplus
NHFA solution that is not adsorbed on the surface of the CNT; and
drying the field effect transistor to stably adsorb the ions to the
surface of the CNT.
7. The method of claim 6, further comprising: forming a passivation
layer on the surface of the CNT.
8. The method of claim 1, wherein the gate is made of silicon
oxide.
9. The method of claim 1, wherein the source and the drain are made
of gold (Au).
10. The method of claim 1, wherein the substrate is made of
silicon.
11. A method of controlling a position of ions in a field effect
transistor comprising: doping the carbon nanotube (CNT) of the
field effect transistor according to claim 1; and moving the ions
on the CNT towards the drain or the source by applying a second
voltage between the source and the drain.
12. The method of claim 11, wherein adsorbing the ions includes
dropping a nitronium hexafluoroantimonate (NHFA) solution onto a
surface of the CNT.
13. The method of claim 12, wherein the first voltage is a positive
voltage, the ions are nitronium ions, and the CNT is p-doped.
14. The method of claim 13, wherein the second voltage is a
positive voltage, and the field effect transistor has a forward
direction diode characteristic by moving the nitronium ions towards
the source.
15. The method of claim 13, wherein the second voltage is a
negative voltage, and the field effect transistor has a backward
diode characteristic by moving the nitronium ions towards the
drain.
16. The method of claim 11, wherein a solvent of the NHFA solution
is methanol.
17. The method of claim 12, further comprising: removing the
surplus NHFA solution that is not adsorbed on the surface of the
CNT; and drying the field effect transistor to stably adsorb the
ions to the surface of the CNT.
18. The method of claim 17, further comprising: forming a
passivation layer on the surface of the CNT.
19. A field effect transistor manufactured using the method of
claim 1.
20. A field effect transistor manufactured using the method of
claim 11.
Description
PRIORITY STATEMENT
This application claims priority under U.S.C. .sctn.119 to Korean
Patent Application No. 10-2008-0033882, filed on Apr. 11, 2008, in
the Korean Intellectual Property Office (KIPO), the entire contents
of which are incorporated herein by reference.
BACKGROUND
1. Field
Example embodiments relate to a method of doping a field effect
transistor including carbon nanotubes as a channel, a method of
controlling the position of doping ions, and transistors using the
same.
2. Description of the Related Art
Carbon nanotubes (CNTs) are receiving attention as a next
generation nano semiconductor material that may replace silicon
semiconductors because the CNTs, as a carbon allotrope, have a
one-dimensional structure and show a ballistic transportation
phenomenon. CNTs have improved mechanical and chemical
characteristics, and may be formed to be relatively long in
micrometers with a diameter from a few nanometers to a few tens of
nanometers, and have increased electrical conductivity, and thus,
increased applicability as a fine structure device. Studies have
been conducted to apply CNTs to various devices, and thus, CNTs may
be presently applied to field emission devices, optical
communication fields, and bio devices.
CNTs may be manufactured by using various methods including an arc
discharge method, a laser ablation method, a chemical vapor
deposition (CVD) method using a catalyst, a screen printing method,
or a spin coating method. In order to apply CNTs to semiconductor
devices, e.g., complementary metal-oxide-semiconductor (CMOS)
transistors, p-type and n-type MOS transistors are required, and
CNTs are apt to be p-doped. In the related art, a method of
manufacturing an n-type CNT by doping oxygen or potassium ions has
been disclosed. However, oxygen ions may not be easily separated
from oxygen molecules, and handling the potassium ions may be
difficult.
SUMMARY
To address the above and/or other problems, example embodiments
provide a method of stably doping a carbon nanotube (CNT), which is
a channel of a field effect transistor. Example embodiments also
provide a method of controlling the position of doping ions on a
surface of a CNT of a field effect transistor, and transistors
using the same.
According to example embodiments, a method of doping a carbon
nanotube (CNT) of a field effect transistor may include providing a
source, a drain, the CNT as a channel between the source and the
drain, and a gate on a substrate, applying a first voltage to the
gate, and adsorbing ions on a surface of the CNT.
Adsorbing the ions may include dropping a nitronium
hexafluoroantimonate (NHFA) solution onto a surface of the CNT. The
first voltage may be a positive voltage, the ions may be nitronium
ions, and the CNT may be p-doped. The first voltage may be a
negative voltage, the ions may be hexafloroantimonate ions, and the
CNT may be n-doped. A solvent of the NHFA solution may be methanol,
and the gate may be a back gate.
The method may further include removing a surplus NHFA solution
that is not adsorbed to the surface of the CNT and drying the field
effect transistor to stably adsorb the ions to the surface of the
CNT. The method may further include forming a passivation layer on
the surface of the CNT. The substrate may be made of silicon, the
gate may be made of silicon oxide, and the source and the drain may
be made of gold (Au).
According to example embodiments, a method of controlling a
position of ions in a field effect transistor may include doping
the carbon nanotube of the field effect transistor according to
example embodiments, and moving the ions on the CNT towards the
drain or source by applying a second voltage between the source and
the drain.
BRIEF DESCRIPTION OF THE DRAWINGS
Example embodiments will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings. FIGS. 1-7 represent non-limiting, example
embodiments as described herein.
FIG. 1 is a schematic cross-sectional view of a field effect
transistor having carbon nanotubes (CNT), according to example
embodiments;
FIG. 2 is a cross-sectional view for explaining a method of p-type
doping a field effect transistor, according to example
embodiments;
FIG. 3 is a graph showing the selective removal of metal CNTs from
CNTs of a CNT network structure;
FIG. 4 is a cross-sectional view for explaining a method of
controlling the position of doping ions, according to example
embodiments;
FIGS. 5 and 6 are graphs respectively showing I-V characteristic
curves of p-doped transistors before and after controlling the
position of doping ions in the transistors, according to example
embodiments; and
FIG. 7 is a graph showing an I-V characteristic of a p-doped
transistor after controlling the position of doping ions in the
transistor, according to example embodiments.
It should be noted that these Figures are intended to illustrate
the general characteristics of methods, structure and/or materials
utilized in certain example embodiments and to supplement the
written description provided below. These drawings are not,
however, to scale and may not precisely reflect the precise
structural or performance characteristics of any given embodiment,
and should not be interpreted as defining or limiting the range of
values or properties encompassed by example embodiments. For
example, the relative thicknesses and positioning of molecules,
layers, regions and/or structural elements may be reduced or
exaggerated for clarity. The use of similar or identical reference
numbers in the various drawings is intended to indicate the
presence of a similar or identical element or feature.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
Example embodiments will now be described more fully with reference
to the accompanying drawings in which example embodiments are
shown. In the drawings, the thicknesses of layers and regions are
exaggerated for clarity, and like reference numerals refer to the
like elements. Example embodiments may, however, be embodied in
many different forms and should not be construed as being limited
to the embodiments set forth herein; rather, these embodiments may
be provided so that this disclosure will be thorough and complete,
and will fully convey the concept of example embodiments to those
skilled in the art.
It will be understood that when an element is referred to as being
"connected" or "coupled" to another element, it can be directly
connected or coupled to the other element or intervening elements
may be present. In contrast, when an element is referred to as
being "directly connected" or "directly coupled" to another
element, there are no intervening elements present. As used herein
the term "and/or" includes any and all combinations of one or more
of the associated listed items.
It will be understood that, although the terms "first", "second",
etc. may be used herein to describe various elements, components,
regions, layers and/or sections, these elements, components,
regions, layers and/or sections should not be limited by these
terms. These terms are only used to distinguish one element,
component, region, layer or section from another element,
component, region, layer or section. Thus, a first element,
component, region, layer or section discussed below could be termed
a second element, component, region, layer or section without
departing from the teachings of example embodiments.
Spatially relative terms, such as "beneath," "below," "lower,"
"above," "upper" and the like, may be used herein for ease of
description to describe one element or feature's relationship to
another element(s) or feature(s) as illustrated in the figures. It
will be understood that the spatially relative terms are intended
to encompass different orientations of the device in use or
operation in addition to the orientation depicted in the figures.
For example, if the device in the figures is turned over, elements
described as "below" or "beneath" other elements or features would
then be oriented "above" the other elements or features. Thus, the
exemplary term "below" can encompass both an orientation of above
and below. The device may be otherwise oriented (rotated 90 degrees
or at other orientations) and the spatially relative descriptors
used herein interpreted accordingly.
The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
example embodiments. As used herein, the singular forms "a," "an"
and "the" are intended to include the plural forms as well, unless
the context clearly indicates otherwise. It will be further
understood that the terms "comprises" and/or "comprising," when
used in this specification, specify the presence of stated
features, integers, steps, operations, elements, and/or components,
but do not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components, and/or
groups thereof.
Example embodiments are described herein with reference to
cross-sectional illustrations that are schematic illustrations of
idealized embodiments (and intermediate structures) of example
embodiments. As such, variations from the shapes of the
illustrations as a result, for example, of manufacturing techniques
and/or tolerances, are to be expected. Thus, example embodiments
should not be construed as limited to the particular shapes of
regions illustrated herein but are to include deviations in shapes
that result, for example, from manufacturing. For example, an
implanted region illustrated as a rectangle will, typically, have
rounded or curved features and/or a gradient of implant
concentration at its edges rather than a binary change from
implanted to non-implanted region. Likewise, a buried region formed
by implantation may result in some implantation in the region
between the buried region and the surface through which the
implantation takes place. Thus, the regions illustrated in the
figures are schematic in nature and their shapes are not intended
to illustrate the actual shape of a region of a device and are not
intended to limit the scope of example embodiments.
Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which example
embodiments belong. It will be further understood that terms, such
as those defined in commonly-used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly
so defined herein.
Hereinafter, a method of doping a carbon nanotube (CNT) of a field
effect transistor and a method of controlling the position of
doping ions will be described. FIG. 1 is a schematic
cross-sectional view of a field effect transistor 100 having a
carbon nanotube (CNT), according to example embodiments. Referring
to FIG. 1, a gate insulating layer 11 may be formed on a conductive
substrate 10, for example, a silicon substrate. The gate insulating
layer 11 may be made of silicon oxide having a thickness of about
100 nm. A source electrode 13 and a drain electrode 14 may be
formed on the gate insulating layer 11. The source electrode 13 and
the drain electrode 14 may be separated by about 4 .mu.m, and may
be formed of Au to a thickness of about 20 nm on a Ti adhesive
layer having a thickness of about 10 nm.
A CNT 20 may be disposed between the source electrode 13 and the
drain electrode 14. The CNT 20 may be random network single-walled
carbon nanotubes having a network structure with a width of about
2.5 .mu.m and may be directly grown in situ using a chemical vapor
deposition (CVD) method.
A doping method according to example embodiments may stably dope a
surface of the CNT 20 with ions. In order to dope the surface of
the CNT with ions, a dopant solution may be prepared. The dopant
solution may be readily separated into positive ions and negative
ions, and may be a nitronium hexafluoroantimonate (NHFA) solution.
A solvent may be ethanol, which is readily dried at room
temperature. The NHFA solution may be made by dissolving NHFA
powder in methanol to a concentration of about 1 .mu.M to about 10
.mu.M. Droplets of the NHFA solution may be dropped on the surface
of the CNT 20 using a micro pipette so that the NHFA solution may
be absorbed by the surface of the CNT 20. Each drop may be about
500 .mu.L. Nitronium ions NO.sub.2.sup.+ and hexafloroantimonate
ions SbF.sub.6.sup.- may be separated in the NHFA solution.
FIG. 2 is a cross-sectional view for explaining a method of
p-doping a field effect transistor 200, according to example
embodiments. Referring to FIG. 2, a predetermined or given positive
gate voltage Vg, for example, about 10V, may be applied to the
conductive substrate 10, which is a back gate, and a ground voltage
may be applied to the source electrode 13 and the drain electrode
14. A droplet of the prepared NHFA solution may be dropped on the
CNT 20, which is negatively charged by the gate voltage Vg.
Thus, positive NO.sub.2.sup.+ ions may be adsorbed to the surface
of the CNT 20. The surplus NHFA solution and unnecessary ions may
be drained by tilting the field effect transistor 200. When the
conductive substrate 10 is dried, the positive nitronium ions
NO.sub.2.sup.+ may be stably and ionically adsorbed on the surface
of the CNT 20, and thus, the CNT 20 may be p-doped. A passivation
layer 30 that stabilizes the adsorption of the positive ions on the
CNT 20 may further be formed on the CNT 20. The passivation layer
30 may be formed of a photoresist material, for example, polymethyl
methacrylate (PMMA).
FIG. 3 is a graph showing the selective removal of metal CNTs from
CNTs of a CNT network structure. Referring to FIG. 3, when a
voltage of about 0.5V is applied to the drain electrode 14 of the
field effect transistor 100 of FIG. 1, from the I-V characteristic
plot P1, the drain current Ids may be hardly modulated and may be
maintained at a relatively high level regardless of the variation
of the gate voltage Vgs. The metal CNTs and the semiconductor CNTs
may be mixed in the CNT network structure and the current
characteristic of the field effect transistor 100 may be dominated
by the metal CNTs.
In the field effect transistor 200 in which a droplet of about 1 mM
NHFA solution is dropped on the CNT 20, when a voltage of about
0.5V is applied to the drain electrode 14, from the I-V
characteristic plot P2, the drain current Ids may have a ON/OFF
ratio of about 10.sup.3, which is clearly modulated. Also, the
drain current Ids may be reduced, and the metal CNTs may be
selectively removed from the CNT network structure.
In example embodiments, a method of p-doping a transistor (CNT) has
been described, and hereinafter a method of n-doping the transistor
will now be described. In order to n-dope a transistor, a
predetermined or given negative voltage, for example, a gate
voltage of about -10V, may be applied to the conductive substrate
10 which is a back gate, and a ground voltage may be applied to the
source electrode 13 and the drain electrode 14. A droplet of the
prepared NHFA solution may be dropped on the CNT 20. The CNT 20 may
be positively charged by the gate voltage, and thus,
hexafloroantimonate ions SbF.sub.6.sup.- may be adsorbed to the
surface of the CNT 20. Then, surplus NHFA solution and unnecessary
ions may be drained by tilting the field effect transistor 100.
When the conductive substrate 10 is dried, hexafloroantimonate ions
SbF.sub.6.sup.- may be stably adsorbed to the surface of the CNT
20, and thus, the CNT 20 may be n-doped.
FIG. 4 is a cross-sectional view for explaining a method of
controlling the position of doping ions in a field effect
transistor 300 according to example embodiments. Referring to FIG.
4, a predetermined or given positive voltage, for example, a gate
voltage Vg of about 10V, may be applied to the conductive substrate
10, which is a back gate, and a ground voltage may be applied to
the source electrode 13 and the drain electrode 14. A droplet of
the prepared NHFA solution may be dropped on the CNT 20. The CNT 20
may be negatively charged by the gate voltage Vg, and thus,
nitronium ions NO.sub.2.sup.+ may be adsorbed to the surface of the
CNT 20.
Then, when a voltage of about +1V is applied to the drain electrode
14, a majority of the positive ions on the CNT 20 may be moved away
from the drain electrode 14 towards the source electrode 13. Thus,
the position of the positive ions may be controlled to be
positioned towards the source electrode 13. The increase in the
positive ions on the source electrode 13 may form a Schottky
barrier between the source electrode 13 and the CNT 20. Surplus
NHFA solution and unnecessary ions may be drained by tilting the
field effect transistor 300.
When the conductive substrate 10 is dried, the nitronium ions
NO.sub.2.sup.+ may be stably adsorbed on the surface of the CNT 20,
on a side near the source electrode 13. The passivation layer 30
that stabilizes the adsorption of the positive ions on the CNT 20
may further be formed on the CNT 20. The passivation layer 30 may
be formed of polymethyl methacrylate (PMMA).
FIGS. 5 and 6 are graphs showing I-V characteristic curves of the
field effect transistor 200 before controlling the position of the
ion doping and the p-doped field effect transistor 300 after
controlling the position of ion doping, according to example
embodiments. Referring to FIG. 5, if the I-V characteristic curve
is seen after applying a voltage of about 1V to about -1V to the
drain electrode 14, when a gate voltage Vgs is applied to the field
effect transistor 200 in a negative direction, the field effect
transistor 200 may be turned on. For example, the field effect
transistor 200 may be a p-type transistor.
Referring to FIG. 6, the field effect transistor 300 may be turned
on when positive voltages of about 0.5V and about 1V are applied to
the drain electrode 14, however, the field effect transistor 300
may not be turned on when a voltage of equal to and less than about
0V is applied to the drain electrode 14. A Schottky barrier may be
formed between the source electrode 13 and the CNT 20 because
positive ions on the surface of the CNT 20 may have moved towards
the source electrode 13. Thus, the field effect transistor 300
shows a forward direction diode characteristic. In example
embodiments, a method of controlling the position of positive ions
towards the source electrode 13 is described. Hereinafter, a method
of controlling the position of positive ions towards the drain
electrode 14 will be described. A predetermined or given positive
voltage, for example, a gate voltage of about 10V, may be applied
to the conductive substrate 10, which is a back gate, and a ground
voltage may be applied to the source electrode 13 and the drain
electrode 14. A droplet of prepared NHFA solution may be dropped on
the CNT 20. The CNT 20 may be negatively charged by the gate
voltage, and thus, positive nitronium ions NO.sub.2.sup.+ may be
adsorbed on the surface of the CNT 20. Then, when a voltage of
about -1V is applied to the drain electrode 14, a majority of the
positive ions on the CNT 20 may move toward the drain electrode 14.
Thus, the position of the positive ions may be controlled to be
towards the drain electrode 14. The increase in the positive ions
on the drain electrode 14 may form a Schottky barrier between the
drain electrode 14 and the CNT 20.
The surplus NHFA solution and unnecessary ions may be drained by
tilting the field effect transistor 200. When the conductive
substrate 10 is dried, the positive nitronium ions NO.sub.2.sup.+
may be stably and ionically adsorbed on the surface of the CNT 20,
on a side near the source electrode 13. The passivation layer 30
that stabilizes the adsorption of the positive ions on the CNT 20
may further be formed on the CNT 20. The passivation layer 30 may
be formed of polymethyl methacrylate (PMMA).
FIG. 7 is a graph showing an I-V characteristic of a p-doped
transistor after controlling the position of doping ions in the
transistor, according to example embodiments. Referring to FIG. 7,
the field effect transistor 300 may be turned on when negative
voltages of about -0.5V and about -1V are applied to the drain
electrode 14, however, the field effect transistor 300 may not be
turned on when a voltage equal to and greater than about 0V is
applied to the drain electrode 14. A Schottky barrier may be formed
between the drain electrode 14 and the channel 20 because positive
ions on the surface of the CNT 20 may move towards the drain
electrode 14. Thus, the field effect transistor 300 shows a
backward direction diode characteristic.
In example embodiments, the method of controlling the positive ions
in the p-doped transistor is described. However, the position of
the negative ions in an n-doped transistor may be controlled in the
same manner, and thus, the detailed description thereof will not be
repeated. In a method of doping a field effect transistor including
a CNT, according to example embodiments, the CNT may be stably
p-doped and n-doped on the field effect transistor, and thus, a
p-type transistor and an n-type transistor may be readily
manufactured. Also, in the method of controlling the position of
ions in a field effect transistor, a field effect transistor having
a forward or backward diode may be readily manufactured.
While example embodiments have been particularly shown and
described with reference to example embodiments thereof, it will be
understood by one of ordinary skill in the art that various changes
in form and details may be made therein without departing from the
spirit and scope of the following claims.
* * * * *